1. Technical Field
The present invention relates to data communications in general, and in particular to data communications utilizing modems. Still more particularly, the present invention relates to a method for handling data transmissions within a modem.
2. Description of Related Art
The use of an analog modulator-demodulator (modem) to transmit digital signals across an analog channel, such as a telephone line, is well known in the art. Typically, an analog modem transmits data from a local asynchronous data terminal equipment (DTE) to a remote asynchronous DTE at the data rate of the modem's analog channel. In addition, a compression scheme is commonly utilized within a modem for storing and transmitting data in a reduced data format such that data can be communicated more efficiently. In order to compress data, a selected portion of the data must be accumulated initially. Then, the data are compressed to a selected codeword combination. When the compressed data is received at a receiving modem, the selected codeword combination is subsequently decompressed to yield the original data.
A compression scheme promulgated by the International Telecommunications Union (ITU) for data communications over a telephone network is known as the V.42bis standard, the pertinent of which is incorporated herein by reference. The compression scheme under the V.42bis standard includes two transmission modes: a transparent mode and a compressed mode. There are commands that can be sent to a decoder in both transmission modes for mode switching. For example, when in the transparent mode, a two-character sequence, which begins with a special escape character followed by an ECM (i.e., enter compression mode) command, instructs the decoder to switch to the compressed mode. When in the compressed mode, an ETM (i.e., enter transparent mode) command instructs the decoder to switch to the transparent mode.
The present invention provides a method for handling data transmissions within a modem that is operating under the V.42bis standard.